Sword - 1 hit
The Vacuum Mouth is an enemy in Link's Awakening.
There are only three Vacuum Mouths in the game.
The first one appears in the Bottle Grotto, in a room along with three Keese. The first Vacuum Mouth is located at the bottom-left corner of this room, and it will use an ability that sucks you in like a vacuum, hence its name. It will most likely suck Link towards the corner, or to the holes. Vacuum Mouths can also suck up enemies, killing them in the process. It's sucking ability will only last a few seconds and then turn off, before turning on again. If Link wants to kill it, he can make a suicide jump with Roc's Feather and hit it with a Sword slash. If he lands on top of the vacuum, he'll automatically be taken to the very beginning of the dungeon.
The second one appears in the Key Cavern, in the room to the right of the entrance. This Vacuum Mouth has the opposite ability from the first one. It prevents Link from being able to approach by expelling using an ability that pushes him away instead of sucking him up like the previous Vacuum Mouth. Use the Pegasus Boots to dash quickly across the screen and hit this Vacuum Mouth to defeat it.
The third Vacuum Mouth is found in Turtle Rock and behaves by drawing Link to it, while also serving as a partial obstacle for Link. This Vacuum Mouth also has a brief off period making timing essential in order to access a nearby Treasure Chest.